universal-ebml
v0.2.2
Published
Universal ebml parser with custom schema support. It allows you to easily create your own extensible, structural, streamable binary serialization specific for your objects.
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Readme
EBML
EBML stands for Extensible Binary Meta-Language and is somewhat of a binary version of XML. It's used for container formats like webm or mkv.
This fork supports universal schema - you can create your own document structure specific to your project.
install
npm install universal-ebml --save
usage
The Decoder(options, schema)
class is implemented as a Node Transform stream. As input it takes ebml. As output it emits a sequence of chunks: two-element arrays looking like this example.
[ "tag",
{
name: "TimecodeScale",
type: "u",
value: 1000000
}
]
The first element of the array is a short text string. For tags containing values, like this example, the string is 'tag'
.
ebml also has nesting tags. The opening of those tags has the string 'start'
and the
closing has the string 'end'
.
The second element of the array is an object with these members, among others:
name
is the Matroska Element Name.type
is the data type.u
: unsigned integer. Some of these are UIDs, coded as 128-bit numbers. Can be BigNum (bn.js)i
: signed integer. Can be BigNum (bn.js)f
: IEEE-754 floating point number.s
: printable ASCII text string.8
: printable utf-8 Unicode text string.d
: a 64-bit signed timestamp, in nanoseconds after (or before)2001-01-01T00:00UTC
. Can be BigNum (bn.js)b
binary data, otherwise uninterpreted.
value
is the value of the data in the element, represented as a number or a string. Integers stored in 6 bytes or less are represented as numbers, and longer integers are represented as hexadecimal text strings.data
is the binary data of the entire element stored in aUint8Array
.
examples
This example reads a media file into memory and decodes it. The decoder
invokes its data
event for each Element.
See more comprehensive example with custom schema at https://github.com/TiesNetwork/universal-ebml/blob/master/example.js .
const ebml = require('./index.js');
const fs = require('fs');
const schema = require('./test/mkv_schema'); //Matroska schema for tests
const decoder = new ebml.Decoder(null, schema);
decoder.on('data', function(chunk) {
console.log(chunk);
});
fs.readFile('test/media/test.webm', function(err, data) {
if (err)
throw err;
decoder.write(data);
});
This example does the same thing, but by piping the file stream into the decoder (a Transform stream).
const ebml = require('./index.js');
const ebmlDecoder = new ebml.Decoder(null, schema);
const schema = require('./test/mkv_schema'); //Matroska schema for tests
const counts = {};
require('fs').createReadStream('test/media/test.webm')
.pipe(ebmlDecoder)
.on('data', chunk => {
console.log (chunk);
const name = chunk[1].name;
if (!counts[name]) counts[name] = 0;
counts[name]++;
})
.on('finish', () => {
console.log(counts);
});
state of this project
Parsing works, encoder works, user defined schema works. If anything doesn't, please create an issue.
license
MIT
contributors
(in alphabetical order)